Impulsivity is a broadly defined multidimensional personality trait that has been associated with all aspects of drug abuse, including initial drug taking, the transition from initial to repeated use, and relapse. In particular, impulsivity has been associated with the use of the psychostimulant cocaine, and chronic use of cocaine has been associated with enhanced expression of impulsiveness. Despite this connection, the exact nature of the relationship between impulsivity and cocaine use is not well understood, and whether impulsivity is a factor leading to, or resulting from, cocaine use is not known. In addition, both impulsivity and many of the behavioral and neurochemical effects of cocaine are regulated by the 5-HT2 receptor system, yet how the 5- HT2 receptor system mediates the relationship between impulsivity and cocaine use is poorly understood. Well-developed animal models exist to examine various aspects of impulsivity in rodents. Despite this, few attempts have been made to study the effects of acute and chronic cocaine in these animal models. Therefore the purpose of the present proposal is to examine how cocaine and the 5-HT2 receptor system modulate behavior in animal models of impulsivity. [unreadable] [unreadable] [unreadable]